Method of vaporizing solid organometallic compound

ABSTRACT

A method of vaporizing a solid organometallic compound in which the method comprises filling the solid organometallic compound into a container, introducing a carrier gas to the container and taking out the gas containing the organometallic compound, wherein the solid organometallic compound is in the form of pellets and contains an inert support.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of vaporizing from containeran organometallic compound which is solid at normal temperature.Specifically, the invention relates to a method of vaporizing a solidorganometallic compound in a container wherein the solid organometalliccompound is vaporized at a constant concentration and the remainingamount of the solid organometallic compound in the container iseffectively reduced.

2. Description of the Related Art

An organometallic compound such as trimethylindium is useful, forexample, as a raw material for a compound semiconductor. Generally, acontainer filled with an organometallic compound is disposed in atemperature-controlled bath at predetermined temperature, a carrier gassuch as hydrogen is introduced into the container so as to contact withthe organometallic compound in the container, and then the gascontaining the organometallic compound of predetermined concentration istaken out of the container to vaporize the organometallic compound to aproduction apparatus for a compound semiconductor.

A cylindrical container made of stainless steel is typically used as thecontainer, and the container having various characteristics in thestructure of the bottom, an inlet tube of carrier gas, an outlet tube ofthe gas or the like has been known for improving thermal efficiency,controllability of concentration of an organometallic compound, usagerate of the organometallic compound in the container and the like. Thelarger-sized container has been used from the viewpoint of productivityimprovement.

In the case where an organometallic compound is solid at normaltemperature, the compound is filled into the container in the shape ofsmall grains, or the organometallic compound supported on an inertsupport obtained by rotating an inert support and a moltenorganometallic compound is filled into the container.

In the case of being filled an organometallic compound in the shape ofsmall grains into the container, a constant concentration of theorganometallic compound in the gas to be vaporized can not be performed,because it is difficult to maintain the contact condition between acarrier gas and an organometallic compound uniform, caused by becoming asmaller grain size by vaporization or accumulating on the bottom of thecontainer to form a flow path for passing the carrier gas.

In the case where an organometallic compound is filled into a containerin the shape of being supported by the inert support, the organometalliccompound is not supported uniformly and sufficiently, so that a constantconcentration of the organometallic compound is not continuouslyvaporized to occasionally lower usage rate of the organometalliccompound in the container.

A method containing a step of filling a supporting material having aporosity of 50 to 80% by volume into a container by 50 to 80% by volumewith respect to the container capacity, a step of filling a granularsolid material of an organometallic compound into the container, and astep of supporting in the container by melting and rotating the supportmaterial and the organometallic compound, has been known as an exampleof a support method (refer to JP No. 8-299778 A).

However, even this method is not necessarily sufficient, and a method ofvaporizing a solid organometallic compound has been desired such that anorganometallic compound which is solid at normal temperature can bevaporized at a constant concentration and the usage rate of theorganometallic compound can be improved.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method of vaporizinga solid organometallic compound wherein an organometallic compound whichis solid at normal temperature can be vaporized at a constantconcentration, the usage rate of the solid organometallic compound inthe container can be improved, that is, the remaining amount of thesolid organometallic compound in the container is effectively reduced.

Through earnest studies for a method of vaporizing a solidorganometallic compound such that an organometallic compound which issolid at normal temperature can be vaporized at a constantconcentration, the usage rate of the solid organometallic compound inthe container can be improved, the inventors of the present inventionhave reached the present invention by finding out that pellets of asolid organometallic compound containing an inert support are filledinto the container, so that an organometallic compound which is solid atnormal temperature can be vaporized at a constant concentration, theusage rate of the solid organometallic compound in the container can beimproved.

That is to say, the present invention is a method of vaporizing a solidorganometallic compound such that an organometallic compound which issolid at normal temperature, in which the method comprises filling thesolid organometallic compound into a container, introducing a carriergas to the container and taking out the gas containing theorganometallic compound, wherein the organometallic compound is in theform of pellets and contains an inert support.

The pellets to be used are previously molded in such a manner that aninert support and a solid organometallic compound are filled into pluralrecessed portions in the shape of pellets provided on a molding plateand then the solid organometallic compound is hot-melted and thereaftersolidified by cooling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an example of a containerfilled with pellets; and

FIG. 2 is a graph showing the results in Example 1 and ComparativeExample 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A solid organometallic compound in the present invention is useful, forexample, as a raw material for a compound semiconductor by a vapor phasegrowth method; examples thereof include indium compounds such astrimethylindium, dimethylchloroindium, cyclopentadienylindium,trimethylindium.trimethylarsine adduct andtrimethylindium.trimethylphosphine adduct, zinc compounds such asethylzinc iodide, ethylcyclopentadienylzinc and cyclopentadienylzinc,aluminum compounds such as methyldichloroaluminum, gallium compoundssuch as methyldichlorogallium, dimethylchlorogallium anddimethylbromogallium, and biscyclopentadienylmagnesium.

Examples of an inert support to be used include ceramics such asalumina, silica, mullite, glassy carbon, graphite, potassium titanate,quartz, silicon nitride, boron nitride and silicon carbide, and metalssuch as stainless steel, aluminum, nickel and tungsten.

Examples of the shape of the support to be used include, but are notparticularly limited to, various shapes such as indeterminate forms,globular shape, fibrous shape, reticular shape, coil shape, cylindricalshape and tubular shape.

Examples of the surface of the support include a smooth surface, asurface with minute irregularities and a surface with many pores (voids)in the carrier itself. Examples of such a support include alumina balls,Raschig ring, heli pack, Dickson packing, stainless steel sinteredelement and metal wool.

The shape of pellets is not particularly limited but yet examplesthereof include spherical shape, hemispherical shape, trapezoidal shape,ellipsoidal shape, cylindrical shape and prismatic shape.

The size of pellets of an organometallic compound containing an inertsupport is approximately 3 to 20 mm, preferably approximately 5 to 10mm. This size signifies the maximum length among lengths typifying theshape of pellets, for example, which size signifies the diameter in thecase of spherical shape, the major axis in the case of ellipsoidalshape, a longer length among the diameter of the under surface and theheight in the case of trapezoidal shape, and a longer length among thediameter of the circle and the length of the column in the case ofcylindrical shape.

The pellets are molded in such a manner that an inert support and asolid organometallic compound are filled into plural recessed portionsin the shape of pellets provided on a molding plate and then the solidorganometallic compound is hot-melted and thereafter solidified bycooling.

An inert support smaller than the shape of pellets are filled intoplural recessed portions in the shape of pellets, and subsequently smallparticles or ground product of a solid organometallic compound arefilled thereinto. On this occasion, an inert support may be filled aftera solid organometallic compound is filled.

A top cover is disposed on the filled inert support and solidorganometallic compound, and fixed by pressing thereagainst. The fixingis performed by a clamp or the like.

A molding plate whose recessed portions are filled with the inertsupport and solid organometallic compound, and other molding plate whoserecessed portions are filled with the solid organometallic compound maybe superposed and fixed so that the positions of the recessed portionscorrespond to each other.

Next, a molding plate in which a top cover is disposed on the filledinert support and solid organometallic compound is put in a containerfor heating and cooling, which is sealed up.

The filling of the inert support and solid organometallic compound intothe recessed portions of a molding plate as well as the sealing of themolding plate into a container for heating and cooling are performedunder an inert gas atmosphere such as nitrogen, argon and neon, forexample, in a glove box to prevent the solid organometallic compoundfrom contacting with oxygen or moisture.

The oxygen concentration in the atmosphere is approximately 1 ppm(volume) or less, preferably approximately 0.1 ppm (volume) or less, andit is desirable that the oxygen concentration is always monitored by anoximeter. Commercially available products can be used for an oximeter.

It is important that oxygen, moisture and other volatile impurities aresufficiently removed from the inert support, apparatus and tools to beused, and it is desirable that the inert support, apparatus and toolsare subject to vacuum degassing while heated at temperatures in apermissible range, and thereafter voids thereof are replaced with inertgas such as nitrogen and argon.

A container for heating and cooling with the molding plate sealed is putin a heating furnace to melt the inside solid organometallic compound byheating. The temperature of the heating furnace is the melting point orhigher of the organometallic compound, typically higher than the meltingpoint by approximately 10 to 25° C., preferably approximately 15 to 20°C., which temperature is maintained for approximately 1 to 5 hours,preferably approximately 2 to 3 hours to completely melt theorganometallic compound, which is closely adhered to the inert supportto form the shape of pellets.

Subsequently, the container for heating and cooling containing the solidorganometallic compound put is taken out of the heating furnace andimmersed in a cold medium (typically, water is used) to solidify theinside solid organometallic compound by cooling.

Thereafter, the container for heating and cooling containing the solidorganometallic compound is put in inert gas atmosphere such as a glovebox to take the molding plate out of the container for heating andcooling and take off the top cover, which molding plate is vibrated totake pellets of the solid organometallic compound containing the inertsupport out of the recessed portions. The obtained pellets of the solidorganometallic compound containing the inert support are typicallystored in a storage container.

Previously molded pellets of the solid organometallic compoundcontaining the inert support are filled into a container to introduce acarrier gas and take the gas containing the organometallic compound ofpredetermined concentration out of the container, which gas is supplied.

FIG. 1 shows a schematic cross-sectional view of an example of acontainer filled with pellets.

A tubular container having the curved bottom is used for a container 1.A carrier gas inlet tube 2 and a carrier gas outlet tube 3 are installedin the upper part of the container 1, and the tip 6 of the carrier gasinlet tube is disposed while inclined by approximately 20 to 50°,preferably approximately 25 to 45°, diagonally downward with respect tothe horizontal direction. The tip 7 of the carrier gas outlet tube isdisposed at the bottom of the container. Pellets 5 of a solidorganometallic compound containing an inert support are filled into thecontainer from a pellet filling opening 4.

The carrier gas inlet tube 2 and the carrier gas outlet tube 3 areinstalled in the upper part of the container in FIG. 1 but yet may beinstalled in the side part of the container if the tip 6 of the carriergas inlet tube is disposed in the upper part of the container and thetip 7 of the carrier gas outlet tube is disposed at the bottom of thecontainer.

The tip 6 of the carrier gas inlet tube is preferably disposed whileinclined by approximately 20 to 50° diagonally downward with respect tothe horizontal direction and inclined against a side wall of thecontainer from a position away from the central axis of the container.

The filled quantity of the pellets 5 of a solid organometallic compoundcontaining an inert support into the container 1 is typicallyapproximately 50 to 90% by capacity of the container with expectation ofthe lower part from the tip of the carrier gas inlet tube.

The container having the curved bottom is shown but yet the container isnot particularly limited thereto and a conical container is also usable.The container having the curved bottom is preferably used in view ofbeing easily manufactured and being capable of supplying gas at constantconcentration and at high efficiency.

A space between the bottom of the container and the tip 7 of the carriergas outlet tube is approximately 2 to 15 mm, preferably approximately 2to 10 mm and more preferably approximately 2 to 5 mm. A space of morethan approximately 15 mm may deteriorate the usage rate of theorganometallic compound.

The container 1 filled with the pellets 5 of a solid organometalliccompound containing an inert support is transported to a place to useit, the carrier gas outlet tube 3 is connected to a vapor phase growthdevice (not shown in the drawing) and the carrier gas inlet tube 2 isconnected to a supply source of carrier gas such as hydrogen gas througha flowmeter (not shown in the drawing) or the like.

The container is retained at constant temperature by atemperature-controlled bath to supply a carrier gas of constant flowrate and shift the carrier gas from the upper part to the lower part ofthe container through a gap between the pellets of a solidorganometallic compound, so that the carrier gas containing theorganometallic compound of constant concentration at the temperature issupplied to a vapor phase growth device or the like through the carriergas outlet tube 3.

According to the above-mentioned method of the present invention, anorganometallic compound which is solid at normal temperature can bevaporizing at a constant concentration and the remaining amount of thesolid organometallic compound in the container is effectively reduced.The method of the present invention is effective also in a large-sizedcontainer.

EXAMPLES

The examples of the present invention are described below and thepresent invention is not limited thereto.

Example 1 Production of Pellets

A molding plate made of polytetrafluoroethylene (PTFE) with an outsidediameter of 150 mmf×a thickness of 8 mm having 349 pieces of recessedportions in the trapezoidal shape (top surface (plate surface): 5 mmf,under surface (plate inside): 4 mmf, height: 5 mm) was used to putDickson packing (3 mmf×3 mm, 0.022 g/piece) in each of the recessedportions, which were next filled uniformly with 0.158 g on average of aground product obtained by grinding solid trimethylindium (hereinafter,occasionally referred to as TMI). A top cover made ofpolytetrafluoroethylene (PTFE) with an outside diameter of 144 mmf×athickness of 3 mm was disposed thereon and put in a heating and coolingcontainer (made of stainless steel), which was sealed up.

Next, the container for heating and cooling was put in a heating furnaceto set heating temperature at 106° C. and start heating up. Afterreaching the preset temperature, the temperature was retained forapproximately 2.5 hours to completely melt the TMI, which was made toinvade the inside of the Dickson packing and then closely adherethereto. The container for heating and cooling was taken out of theheating furnace, immersed in water and cooled to room temperature overapproximately 2 hours to solidify the inside TMI by cooling.

The molding plate was taken out of the container for heating and coolingto take off the top cover and perform the mold release of the molded TMIpellets from the recessed portions by adding vibration to the moldingplate. The obtained TMI pellets were put in a storage container.

The processes except heating and cooling of the container for heatingand cooling including the TMI were performed in a glove box replacedwith argon gas. The inside of the glove box was repeatedly replaced withvacuum and argon gas to maintain the oxygen density at 1 ppm (capacity)or less and perform the processes while always supplying argon gas.

The apparatuses to be used such as Dickson packing, molding plate, topcover, container for heating and cooling and storage container weresubject to vacuum degassing while heated in order to sufficiently removeoxygen and moisture therefrom, and voids thereof were used afterreplaced with argon.

(Supply of TMI)

103.8 g of the above-mentioned TMI pellets (TMI content: 88.4 g)obtained by molding were put in the same container (outside diameter:60.5 mm, height: 120 mm, capacity: 230 ml, tilt angle of the tip ofcarrier gas inlet tube: 500 in the central axis direction) as acontainer shown in FIG. 1 in the glove box replaced with argon gas.

The container was taken out of the glove box to sequentially connect ahydrogen cylinder and a flow control device to the carrier gas inlettube side, and sequentially connect a gas densitometer, a cryogenic trapfor collecting TMI, a pressure control device and a vacuum pump to thecarrier gas outlet tube side.

The container was put in a constant temperature bath and retained at atemperature of 25° C. An epison concentration meter (manufactured byThomas Swan Scientific Equipment Ltd.) was used as the gas concentrationmeter.

Hydrogen gas as a carrier gas was supplied from the hydrogen cylinder atapproximately constant 400 ml/minute (in terms of atmospheric pressure)to vaporize the TMI and regularly measure the TMI concentration in thehydrogen gas with the gas concentration meter. The usage rate (%) of theTMI was calculated from the hydrogen gas flow rate and TMIconcentration. The results are shown in FIG. 2.

The hydrogen gas can be supplied to a usage rate of approximately 85% atapproximately constant 0.234% by capacity without lowering the TMIconcentration.

Comparative Example 1

120.2 g of alumina balls of 4 mmf (manufactured by Fujimi Incorporated)as an inert support and 86.1 g of a ground product of TMI were filledinto the same container as used in Example 1 in a glove box replacedwith argon gas.

This container was leveled in a heated oven and heated to a temperatureof 106° C. while rotated. After retaining at this temperature forapproximately 2 hours, the heating was stopped to cool the container upto room temperature gradually over approximately 5 hours while rotatingin that state, and then solidify and support the TMI on the surface ofthe alumina balls.

In the container including the TMI supported by these alumina balls,similarly to Example 1, a hydrogen cylinder and a flow control devicewere sequentially connected to the carrier gas inlet tube side, and agas densitometer, a cryogenic trap for collecting TMI, a pressurecontrol device and a vacuum pump were sequentially connected to thecarrier gas outlet tube side to supply hydrogen gas at approximatelyconstant 400 ml/minute (in terms of atmospheric pressure), vaporize theTMI and regularly measure the TMI concentration in the hydrogen gas witha gas concentration meter. The results are shown in FIG. 2.

The TMI concentration was being lowered little by little and the usagerate was abruptly lowered from approximately 80%.

1. A method of vaporizing a solid organometallic compound in which themethod comprises filling the solid organometallic compound into acontainer, introducing a carrier gas to the container and taking out thegas containing the organometallic compound, wherein the solidorganometallic compound is in the form of pellets and contains an inertsupport.
 2. The method of vaporizing a solid organometallic compoundaccording to claim 1, wherein the pellets are previously molded in sucha manner that the inert support and the solid organometallic compoundare filled into plural recessed portions in a shape of the pelletsprovided on a molding plate and then the solid organometallic compoundis hot-melted and thereafter solidified by cooling.
 3. The method ofvaporizing a solid organometallic compound according to claim 1, whereina size of the pellets is 3 to 20 mm, represented by a maximum lengthamong lengths typifying a shape of the pellets.
 4. The method ofvaporizing a solid organometallic compound according to claim 1, whereinthe solid organometallic compound is trimethylindium.